CHAPTER 11.-^ 



Morphology' of bacteria— (jrouping— Mode of multiplication — Spore-forma- 

 tion— Motility. 



In structure the bacteria are unicellular, and are seen 

 to exist as spherical, rod- or spiral-shaped bodies. 

 They always develop from pre-existing cells of the same 

 character and never appear spontaneously. 



The classifications of the older authors and of the 

 botanists are usually upon purely morphological pecu- 

 liarities, and in consequence are more or less compli- 

 cated. The present tendency is to simplif}^ this mor- 

 phological classification, and to bring the bacteria into 

 three great groups, with their subdivisions ; each group 

 comprising those members whose individual outline is 

 that either of a sphere, a rod, or a spiral. 



To these three grand divisions are given the names 

 cocci or micrococci, bacilli, and spirilla. 



In the group micrococci belong all spherical forms, ' 

 i. e., all those forms the isolated individual members of 

 which are of equal diameter in all directions. (See Fig. 

 1, a 6 c d.) 



The bacilli comprise all oval or rod-formed bacteria. 

 (See Fig. 2.) 



To the spirilla belong all organisms that are curved 

 when seen in short segments, or when in longer threads 

 are twisted in the form of a corkscrew. (See Fig. 3.) 



The micrococci are subdivided according to their 

 grouping, as seen in growing cultures, into staphylococci 



' Morphology, pertaining to shape ; outline. 



